Have we finally solved the fairy circle mystery?

Scientists used to think that these strange circular patches were made by termites. New research suggests otherwise.

Theories about what causes fairy circles have ranged from radiation to plant toxins, but a new idea is elbowing other ideas aside. (Photo: Stephan Getzin/Helmholtz Centre for Environmental Research)

One of the most perplexing phenomena of the natural world occurs in Namibia, where strange circular patches of barren land occur in the middle of arid grasslands. According to local oral tradition, these "fairy circles" are the footprints of the gods or possess magical powers.

The exact explanation for these fairy circles has remained unclear for centuries. Theories over the years have included everything from radiation to plant toxins. Most recently, some scientists have suggested that the fairy circles could have been caused by one or two species of termites that chewed up plant roots and left nothing behind to grow. In fact, a 2013 study found that these termites were indeed present at the vast majority of fairy circles, and especially at newer circles. But the question remained, were the insects the cause of the mystery or were they just taking advantage of the situation?

Now we have a new theory. According to research published May 20 in the journal Ecography, the fairy circles appear to be caused by the grasslands around them. It's a form of self-regulation: the nearby grasses suck up all of the available water, leaving some circular bare patches.

How did the the scientists behind the new paper come to this conclusion? The researchers — who have been studying the grasslands of Namibia for 15 years — examined aerial images of the fairy circles and found that they occurred in surprisingly regular patterns. If they had been caused by termites, the authors write, the fairy circles would not appear in such a homogenous distribution and would instead be placed much more randomly. The patterns aren't visible to the naked eye; they show up when the fields are examined statistically.

"The occurrence of such patterning in nature is rather unusual," said Stephan Getzin of the Helmholtz Centre for Environmental Research in a news release. "There must be particularly strong regulating forces at work." That "regulating force" probably takes place below the ground, according to computer models of the region's water resources and plant roots. The researchers showed that competition for water in this arid region results in plant patterns that create the fairy circles.

This isn't conclusive proof, but Getzin said "we consider this at present being the most convincing explanation." This appears to discredit the termite theory, and it may stand as the theory du jour until scientists can observe a fairy circle forming, something that has never been done to date. All known fairy circles have only been observed after they have appeared, so maybe there's something magic in them after all.